The invention relates to a control system for an internal combustion engine, wherein the maximum combustion pressure is controlled by changing the start of injection.
DE 44 46 246 C1, originating from the applicant, discloses a control system for an internal combustion engine. In this system the maximum combustion pressure is controlled by changing the start of injection. Owing to the variable adjustability of the start of injection, the entire acceleration potential of the engine can be utilized, for example when there is a load. However, any errors, for example misfirings, are not taken into consideration in this control process.
Proceeding from the above described prior art, the object of the invention is to improve the control system with respect to operational reliability.
In the control system according to the invention, the maximum combustion pressure is diagnosed by means of outlier recognition. The outlier recognition determines a first or second mode and sets a diagnostic value as a function of the mode. To this end, the outlier recognition calculates a mean value from a first and an nth maximum combustion pressure value and determines for the values between the first and nth maximum combustion pressure their deviation from the mean value. If the deviations can be tolerated, the first mode is set. In the first mode the diagnostic value is then set to the maximum combustion pressure value. If the deviation cannot be tolerated, the second mode is set. In the second mode the diagnostic value is equivalent to the mean value.
The diagnostic value, determined previously, is sent together with a maximum combustion pressure nominal value to an injection start controller, which determines the start of injection from this system deviation. For a negative system deviation, the start of injection is delayed. The system deviation is negative, when the diagnostic value is greater than the nominal value of the maximum combustion pressure. For a positive system deviation, the injection is started earlier. The system deviation is positive, when the diagnostic value is less than the nominal value of the maximum combustion pressure, i.e. when there is still an additional pressure potential available.
The advantage of the invention lies in the fact that stochastic errors, in particular misfirings, are effectively eliminated. Thus, the quality of the control system is significantly increased. A limiting element is provided, according to the invention, as another measure to protect the control system.
One embodiment of the invention provides that an injection start precontrol value is also included in the calculation of the start of injection. This precontrol value of the start of injection is calculated by means of a group of curves. This group of curves represents a function of the engine speed and of a power-determining signal. The power-determining signal is defined, according to the invention, as the quantity of fuel injected or the travel of a control rod. A precontrol has the advantage of a short reaction time to an immediate load change.
The major distinction between the prior art control system and the invention lies in the fact that the feedback control occurs at every engine operating point and not just when there is a load.
The control system, described in the invention, can be installed in internal combustion engines by common rail construction method, PLD construction method (pump-line-nozzle) or a conventional construction method.